2,046 research outputs found
Implications of multiple high-redshift galaxy clusters
To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have
been observed, spectroscopically confirmed and are reported in the literature.
These objects should be exceedingly rare in the standard LCDM model. We
conservatively approximate the selection functions of these clusters' parent
surveys, and quantify the tension between the abundances of massive clusters as
predicted by the standard LCDM model and the observed ones. We alleviate the
tension considering non-Gaussian primordial perturbations of the local type,
characterized by the parameter fnl and derive constraints on fnl arising from
the mere existence of these clusters. At the 95% confidence level, fnl>467 with
cosmological parameters fixed to their most likely WMAP5 values, or fnl > 123
(at 95% confidence) if we marginalize over WMAP5 parameters priors. In
combination with fnl constraints from Cosmic Microwave Background and halo
bias, this determination implies a scale-dependence of fnl at approx. 3 sigma.
Given the assumptions made in the analysis, we expect any future improvements
to the modeling of the non-Gaussian mass function, survey volumes, or selection
functions to increase the significance of fnl>0 found here. In order to
reconcile these massive, high-z clusters with an fnl=0, their masses would need
to be systematically lowered by 1.5 sigma or the sigma8 parameter should be
approx. 3 sigma higher than CMB (and large-scale structure) constraints. The
existence of these objects is a puzzle: it either represents a challenge to the
LCDM paradigme or it is an indication that the mass estimates of clusters is
dramatically more uncertain than we think.Comment: 11 pages, 7 figures, modified to match published versio
Constraints on the equation of state of dark energy and the Hubble constant from stellar ages and the CMB
We place tight constraints on the redshift-averaged, effective value of the
equation of state of dark energy, w, using only the absolute ages of Galactic
stars and the observed position of the first peak in the angular power spectrum
of the CMB. We find w<-0.8 at the 68% confidence level. If we further consider
that w > -1, this finding suggests that within our uncertainties, dark energy
is indistinguishable from a classical vacuum energy term.
We detect a correlation between the ages of the oldest galaxies and their
redshift. This opens up the possibility of measuring w(z) by computing the
relative ages of the oldest galaxies in the universe as a function of redshift,
dz/dt. We show that this is a realistic possibility by computing dz/dt at z~0
from SDSS galaxies and obtain an independent estimate for the Hubble constant,
H_0 = 69 \pm 12 km s-1 Mpc-1. The small number of galaxies considered at z>0.2
does not yield, currently, a precise determination of w(z), but shows that the
age--redshift relation is consistent with a Standard LCDM universe with .Comment: Submitted to Ap
Comparison of Results Following Modified Widman Flap Surgery With and Without Surgical Dressing
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141358/1/jper0470.pd
Intensification of oxidation capacity using chloroalkanes as additives in hydrodynamic and acoustic cavitation reactors
The effect of the presence and absence of the chloroalkanes, dichloromethane (CH2Cl2), chloroform (CHCl3) and carbon tetrachloride (CCl4) on the extent of oxidation of aqueous I- to I3- has been investigated in (a) a liquid whistle reactor (LWR) generating hydrodynamic cavitation and (b) an ultrasonic probe, which produces acoustic cavitation. The aim has been to examine the intensification achieved in the extent of oxidation due to the generation of additional free radicals/oxidants in the reactor as a result of the presence of chloroalkanes. It has been observed that the extent of increase in the oxidation reaction is strongly dependent on the applied pressure in the case of the LWR. Also, higher volumes of the chloroalkanes favour the intensification and the order of effectiveness is CCl4> CHCl3 > CH2Cl2. However, the results with the ultrasonic probe suggest that an optimum concentration of CH2Cl2 or CHCl3 exists beyond which there is little increase in the extent of observed intensification. For CCl4, however, no such optimum concentration was observed and the extent of increase in the rates of oxidation reaction rose with the amount of CCl4 added. Stage wise addition of the chloroalkanes was found to give marginally better results in the case of the ultrasonic probe as compared to bulk addition at the start of the run. Although CCl4 is the most effective, its toxicity and carcinogenicity may mean that CH2Cl2 and CHCl3 offer a safer viable alternative and the present work should be useful in establishing the amount of chloroalkanes required for obtaining a suitable degree of intensification
Managing IS projects in SMEs – Tailoring the PRINCE2TM1 methodology
The history of information systems project management is littered with many well documented disasters, and even more that have not been recorded in the literature for a range of political and commercial reasons. Such failures in the public sector gave rise to the development and deployment of the PRINCE2 project management methodology, which is now used extensively in the public sector and increasingly in the private sector also. PRINCE2 is, however, a ‘big beast’ – a large and quite complex set of concepts, tools, processes and techniques – which can appear rather daunting when undertaking fairly small scale projects in small to medium sized enterprises (SMEs). This paper examines how two companies have adapted the PRINCE2 project management methodology to control information systems (IS) projects in organisations of circa 200 employees, on projects of about 12 months duration. The first case study (Aeroengine Bearings UK Ltd) is implementing a product life cycle management (PLM) system to control and integrate shop floor engineering and design information. In the second case study, a financial services company specialising in electronic funds collection (Allpay.net) has used PRINCE2 to project manage the implementation of a bespoke middleware product that integrates its back office systems that provide customised payment statements to individual clients. Both these business projects were undertaken via the Knowledge Transfer Partnership (KTP) scheme, which supports university academics working with industry on strategic projects.
Field of Research: project management, information systems, SMEs, knowledge transfe
Constraining Cosmological Parameters Based on Relative Galaxy Ages
We propose to use relative galaxy ages as a means of constraining
cosmological parameters. By measuring the age difference between two ensembles
of old galaxies at somewhat different redshifts, one could determine the
derivative of redshift with respect to cosmic time, dz/dt. At high redshifts,
z=1-2, this measurement would constrain the equation-of-state of the dark
energy, while at low redshifts, z< 0.2, it would determine the Hubble constant,
H_0. The selected galaxies need to be passively-evolving on a time much longer
than their age difference.Comment: ApJ, submitted (6/7/01). 12 pages, 4 figure
Mice with Reduced NMDA Receptor Expression Display Behaviors Related to Schizophrenia
AbstractN-methyl-D-aspartate receptors (NMDARs) represent a subclass of glutamate receptors that play a critical role in neuronal development and physiology. We report here the generation of mice expressing only 5% of normal levels of the essential NMDAR1 (NR1) subunit. Unlike NR1 null mice, these mice survive to adulthood and display behavioral abnormalities, including increased motor activity and stereotypy and deficits in social and sexual interactions. These behavioral alterations are similar to those observed in pharmacologically induced animal models of schizophrenia and can be ameliorated by treatment with haloperidol or clozapine, antipsychotic drugs that antagonize dopaminergic and serotonergic receptors. These findings support a model in which reduced NMDA receptor activity results in schizophrenic-like behavior and reveals how pharmacological manipulation of monoaminergic pathways can affect this phenotype
Efficient computation of hashes
The sequential computation of hashes at the core of many distributed storage systems and found, for example, in grid services can hinder efficiency in service quality and even pose security challenges that can only be addressed by the use of parallel hash tree modes. The main contributions of this paper are, first, the identification of several efficiency and security challenges posed by the use of sequential hash computation based on the Merkle-Damgard engine. In addition, alternatives for the parallel computation of hash trees are discussed, and a prototype for a new parallel implementation of the Keccak function, the SHA-3 winner, is introduced
Electronic and Thermoelectric Properties of RuIn_{3-x}A_{x} (A = Sn, Zn)
Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)]
transport measurements on the semiconducting intermetallic system RuIn3 and its
substitution derivatives RuIn_{3-x}A_{x} (A = Sn, Zn). Higher values of the
thermoelectric figure of merit (zT = 0.45) compared to the parent compound were
achieved by chemical substitution. Here, using density functional theory based
calculations, we report on the microscopic picture behind the measured
phenomenon. We show in detail that the electronic structure of the substitution
variants of the intermetallic system RuIn_{3-x}A_{x} (A = Sn, Zn) changes in a
rigid-band like fashion. This behavior makes possible the fine tuning of the
substitution concentration to take advantage of the sharp peak-like features in
the density of states of the semiconducting parent compound. Trends in the
transport properties calculated using the semi-classical Boltzmann transport
equations within the constant scattering time approximation are in good
agreement with the former experimental results for RuIn_{3-x}Sn_{x}. Based on
the calculated thermopower for the p-doped systems, we reinvestigated the
Zn-substituted derivative and obtained ZnO-free RuIn_{3-x}Zn_{x}. The new
experimental results are consistent with the calculated trend in thermopower
and yield large zT value of 0.8.Comment: PRB Accepted, 11 pages, 10 figure
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